Conventionally, for an image forming apparatus such as a copying machine and a printer, the following process has been adopted. Namely, it is the process in which (1) the surface of a photoreceptor (image forming body) is uniformly charged by charging means such as a charging roller, (2) an image is projected onto the photoreceptor from an optical system having a laser irradiation unit and the like to erase a charge in a portion of the photoreceptor that is exposed, and thereby, to form a latent image, (3) toner is supplied to the latent image on the photoreceptor with a developing roller and the like to form a toner image, (4) the toner image is transferred to a recording medium by transferring means, for example, of giving charge from the backside of the recording medium such as paper, and (5) the transferred toner image on the recording medium is fixed by fixing means such as heat and pressure thereby to form a printed image.
In such a process, a mechanism for forming the toner image in item (3) (developing mechanism) is performed, for example, by a mechanism including a developing roller 2 which opposes a photoreceptor drum 3 holding the latent image so as to come into contact with or close to the same, and a toner conveyance roller 1 which opposes the developing roller 2 so as to come into contact with or close to the same and is arranged so as to be in contact with a toner reservoir in a toner cassette as shown in FIG. 4. In the mechanism in FIG. 4, when the individual rollers rotate in the respective directions of the arrows, toner 5 is conveyed by the toner conveyance roller 1 and supplied onto the surface of the developing roller 2. The toner 5 is formed into a uniform thin film by a stratification blade 4. The developing roller 2 having the thin film of the toner 5 on the surface comes into contact with or close to the photoreceptor drum 3 and rotates, and thereby, the toner 5 sticks to the latent image on the photoreceptor drum 3 to form (develop) the toner image.
As mentioned above, the toner conveyance roller is for conveying the toner from the toner reservoir and supplying it onto the developing roller, and for scraping and recovering the toner that is not used and remains on the surface of the developing roller. As the toner conveyance roller, a roller having an elastic foaming body layer on the surface is typically used. A property of conveying toner and properties of supplying and scraping toner in the toner conveyance roller are noticeable performance to obtain a toner image with high quality in the developing mechanism, and conventionally, development of a toner conveyance roller having the excellent performance has been under progress. For example, according to Patent Literature 1, there is developed a roller in which the shape of cells of an elastic layer constituting the roller is set into a shape compressed in the radial direction of the roller in order to secure the nip width between a toner conveyance roller and a developing roller and allow toner not to stick still to the surface of the roller, and the number of cells on the surface of the elastic layer is more than the number of cells inside. Moreover, according to Patent Literature 2, there is developed a toner conveyance roller in which the rotation shaft is set to have a crown shape (drum shape) to allow a foaming body to be a crown shape with a uniform thickness in order to obtain a sufficient property of scraping toner with a property of conveying toner maintained.